1. Field of the Invention
The present invention generally relates to a method and apparatus for dampening pressure ripples or pulses that are produced when drilling a hydrocarbon well and more particularly, to dampening pulses during drilling operations that take place on a drilling ship.
2. Background Art
As a hydrocarbon well is drilled, pressure ripples or pulses are often produced by the drill bit and transmitted up the fluid flow line or mud column to the drilling rig. This pulsation can be very destructive, and if unchecked, can severely damage a drilling rig and associated equipment. Over a period of time, these pulsations will substantially increase maintenance cost, and thereby increase overall drilling costs. The likelihood of damage is substantially increased if the pulsations are a harmonic of the rig structures' resonate frequency. This is especially problematic with respect to drilling performed with a hammer drill bit while drilling offshore or on a drill ship.
In the prior art, a known technique to dampen pulses is to provide a volume or side branch that has zero impedance; that is, is resonant at the proper frequency. If this situation can be arranged, then all of the pulses will pass into the branch and none will pass into the fluid flow line thus, preventing potential damage to the rig or drilling vessel.
Typically, a technique to dampen pulsation is to provide a chamber or side branch near the pump output opening at the rig. In the case of offshore drilling or drilling from a drilling vessel, however, the sources of the pulses down hole can originate from the drill bit. This is particularly true when the drill bit is a hammer drill bit. Known pulsation dampening devices do not have the ability to dampen the destructive pulsations originating from a drill bit. Therefore, a need exists to provide a pulsation dampening apparatus near the drill bit. The present invention overcomes these and other limitations of known pulsation dampening devices.